Nonlinear Growth and Physiological Responses of White Spruce at North American Arctic Treeline

• Main Authors: Lévesque, Mathieu, id_orcid:0 000-0003-0273-510X, Andreu-Hayles, Laia, D'Arrigo, Rosanne, Oelkers, Rose, Buckley, Brendan M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2023
• Subjects: Arctic; Arctic Ocean; Sea ice
• Online Access: https://hdl.handle.net/20.500.11850/610778; https://doi.org/10.3929/ethz-b-000610778

Much is still unknown about the growth and physiological responses of trees to global change at the northern treeline. We combined tree-ring width data with century-long stable carbon and oxygen isotope records to investigate growth and physiological responses of white spruce at two treeline sites in the Canadian Arctic to concurrent increases in temperature, atmospheric CO2 concentration (ca), and decline in sea ice extent over the past century. The tree-ring records were assessed during three periods with contrasting climatic conditions: (a) the early 20th century warming, (b) the 1940–1970 cooling period, and (c) the anthropogenic late 20th century warming period. We found opposing growth trends between the two sites, but similar carbon isotope discrimination (Δ13C) and intrinsic water-use efficiency (iWUE) trajectories. While tree growth (defined as basal area increment) increased at the site nearer to the Arctic Ocean during the 20th century following the rise in temperature and sea ice loss, growth declined after 1950 at the more interior site. At both sites, Δ13C slightly increased over these periods. However, trees showed a nonlinear response to increased ca, shifting after 1970 from a passive stomatal response (i.e., no changes in iWUE) to an active response (i.e., a moderate ∼12% increase in iWUE). Further, our isotope-based findings do not support the idea that temperature-induced drought stress caused the divergent growth trends at our treeline sites. This study thus highlights nonlinear and complex physiological and growth adjustments to concomitant changes in temperature, sea ice extent, and ca over the last century at the northern treeline. ISSN:0148-0227 ISSN:2169-8953 ISSN:2169-8961